The present invention concerns a frame structure or construction for a press section of a paper machine which comprises, in a running direction of a paper web therethrough, first a front frame and then a separate rear frame, with press rolls being mounted on the front and rear frames, at least some of which belonging to a compact press roll combination in which there are press nips between the press rolls through which press fabrics are passed.
In prior art compact press sections of a paper machine, such as the Valmet so-called Sym-Press (.TM.) press section, there have been horizontal beams above the press rolls both at the service side and at the operating side of the paper machine, which connect the front frame and the rear frame of the press section permanently together. In this connection, and also in the following description, the front frame means the frame part that is placed in the direction of running of the web before the compact press roll combination, with a suction roll of the press, e.g., being fixed to the front frame. In a corresponding manner, the rear frame means the frame part placed after the press roll combination.
Difficulties have occurred with respect to replacement both of press fabrics and of press rolls in connection with the prior art frame parts of the press sections. These problems have increased with increase in the widths of the paper machines, in particular due to the fact that the pres rolls have become increasingly longer and heavier. These problems have also been increased by the fact that press fabrics which are made of plastic material and which are rigid over a transverse direction, have started to be used more increasingly. Such press fabrics cannot be jammed into a bundle, because it would thereby become wrinkled and unusable.
Beloit Corporation has attempted to solve the problems described above by means of a so-called "Flip-top" (trademark of Beloit Corporation) frame construction. In this prior art frame solution for a press section, a top frame is used which is provided with a pivot shaft parallel to a transverse direction of the paper machine and placed above the press rolls, whereby either the top part of the front frame or the top part of the rear frame can be opened around the pivot shaft. The two top parts of the frame cannot be opened at the same time. By opening the top part of the front frame, it is possible to facilitate the replacement of the pick-up fabric of the press section and the replacement of the fabric that usually acts as the press fabric in the first nip and in the second nip. The top part of the rear frame is locked thereat, with opening-dumping of the top part of the front frame taking place on support of the rear frame.
Correspondingly, when the top part of the front frame is in the closed-locked position, the top part of the rear frame can be opened or "dumped" so that the press fabric of the third press nip can be replaced. The lower fabric of the first nip, which principally runs in the basement space or area, is replaced by means of arrangements known in and of themselves. The above "Flip-top" solution can be characterized as a sort of "drawbridge" which is opened around an articulated joint expressly situated at a middle of the bridge, while only one half of the bridge can be opened at a time.
Frame constructions for press sections are known from the Valmet Finnish Patent Applications Nos. 844693 (U.S. Pat. Nos. 4,699,692 and 4,608,125) and 854959, in which the front frame and the rear frame are connected to each other and/or to the intermediate frame of the central roll in the press by means of various openable and closeable intermediate frames. Such openable and closeable intermediate frames are usable in themselves, but they increase the cost of manufacture of the frame part because relatively massive frame components must be provided with articulated joints and with means for opening and closing. When compact press roll arrangements are used, problems of space are also encountered because several different press rolls with the auxiliary devices thereof must be accommodated in relatively limited space. This is why it has been necessary to place the frame parts that connect the front frame and the rear frame to each other or to the intermediate frame with the opening and closing means thereof in highly congested spaces, which results in difficulties both for construction and for operation.